The present invention relates to a process for preparing protein-oriented membrane in biochips for use as solar battery, photo sensor, chemosensor and the like. The present invention further relates to an artificial structure comprising the protein-oriented membrane and a photoelectric transducer produced by using the artificial structure.
Various attempts have been made in order to produce so-called biochips utilizing biological functional protein or biological components containing the same.
As one of such biochips, there have been known those utilizing purple membrane from Halobacterium halobium containing a photosensitive protein, bacteriorhodopsin. In the biochips, the component purple membrane is dispersed in a solution, which is then subjected to electrophoresis to form a built-up layer comprising oriented purple membrane on a substrate, namely protein-oriented membrane [see the Preliminary Abstract of 7th SYMPOSIUM ON FUTURE ELECTRON DEVICES, 123-127, Nov. 1-2, 1988, Tokyo, Japan].
The conventional process described above has a disadvantage that protein 1 once adsorbed to a substrate 3 is desorbed therefrom when the substrate 3 with the adsorbed protein 1 is exposed to a solvent, as shown in FIG. 5A. Even if the substrate 3 with the adsorbed protein 1 is not exposed to a solvent, the thus obtained protein-oriented membrane was extremely unstable physically. Therefore, it is very hard to handle and process such membrane. In contrast, in the present invention, as shown in FIG. 5B, the proteins 1 which are adsorbed to the substrate 3 are cross-linked with a crossing linking agent 2 to form a stable, oriented and cross-linked protein membrane as shown in FIG. 1B.
In order to solve the drawback, there has been proposed a structure where an oriented purple membrane 6 formed on a substrate 3 is coated with a polymer film 7, as is shown in FIG. 4 (Japanese Patent Laid-open No. 241432/1988). Because output from the membrane 6, such as electric signal and the like, is taken out through the polymer membrane, the reduction in the output cannot be avoided.
Alternatively, as one of those employing other biological components, there has been also proposed another process where proteoliposomes containing rhodopsin as a photosensitive protein similar to the one described above, are two-dimensionally aligned on a substrate, by utilizing antigen-antibody reaction (Japanese Patent Laid-open No.111428/1988). By the process, it is intended only to form a monolayer consisting of proteoliposome on a substrate. It is not intended at all thereby to produce a photoelectric transducer with a high output, by making the layer into multiple ones. According to the process, it is hard to separate only the produced proteinaceous membrane from a substrate, to process the membrane and to connect it with other electrodes.
There has been also known a process comprising interposing a dried membrane of chromatophores between two electrodes (Japanese Patent Laid-open No. 110224/1989), but a structure produced by the process is not satisfactory either, in terms of physical strength and stability against water, concerning the dried membrane.
Other than those described above, there have been known general processes such as a process for fixing functional protein on a substrate using cross linking agents (Japanese Patent Laid-open No. 132954/1990) and a process referred to as the so-called monomolecular sweeping technique comprising forming Langumuir-Blodgett's membrane (referred to as LB membrane) on water surface, transferring the formed LB membrane onto the surface of an aqueous protein solution, and allowing the protein in the aqueous solution to be adsorbed and be oriented spontaneously onto the surface of the LB membrane (Biochim. Biophys. Acta, 225 (1971), pp. 382). According to the former method, the substrate and the protein membrane are strongly bound with each other, but the protein in the membrane is not oriented. Further, the process does not intend to make the protein membrane into a multiple layer. Accordingly, it is difficult to produce a photoelectric transducer with a higher output. It is impossible to separate the protein membrane from the substrate, to process it or to connect it to other electrodes and the like. The latter process has problem in the physical, chemical stability of the protein-oriented membrane thereby produced.